Michell Instruments Ltd. - PRODUCT NEWS



Dewpoint Measurement of Medical Gases from Michell
Instruments - Update on HTM 02.

This summer saw the release of Health Technical Memorandum (HTM) 02. This document is one in a series of ten published by National Health Service Executive (NHSE) each providing guidance on healthcare specific standards, policies and up to date established best practice. HTM 02 covers the subject of Medical Gas Systems.

HTM 02 is divided in two parts: part A deals with design, installation and validation, while part B deals with operational management. The overall aim is to provide a safe, convenient and cost effective system for the provision of medical gases to the clinical and nursing staff at the point of use.

For the first time HTM regulations give specific information on the specification and measurement of dewpoint or moisture content. The relevant section states:-

"The plant test point and a representative sample of terminal units distributed throughout the pipeline systems should be tested for total water content. The water content must not exceed 67 vpm (equivalent to an atmospheric pressure dew-point of approximately -46 °C). The typical water content of medical gas cylinders is normally below 5 vpm. Water vapour content may be measured using the appropriate test device described in Appendix E (see also paragraph 15.117)".

Whilst paragraph 15.117 tells us:-

"An electronic dew-point meter should be used in preference to water content measurements".

More details are given in paragraph 7.41

"The dryer control system should ensure that regeneration is operated in proportion to the compressed air usage. The effectiveness of the control system will become apparent when the efficiency of the compressor system is tested at 10% and 0% of the system design flow. Evidence of the reliability and performance of a dryer system should be sought from manufacturers, since these items are critical to the overall
performance of the compressor system. The dryer control system should include a dew-point hygrometer and display with a minimum accuracy of ±3 °C in a range from -20 °C to -60 °C atmospheric dew-point, with an alarm set point of -46 °C. (Note that this supersedes the HTM 2022 requirement for an alarm trigger point of 40 °C) It should be arranged that in the event of open circuit, a "plant emergency" alarm be initiated".

Michell Instruments have in the past been extremely active in supplying portable equipment such as the Cermax Portable dewpointmeter. More than 40 instruments have been supplied within the UK, many with sampling systems to allow quick and easy connection to medical gas supplies within hospitals and pharmacies.

Michell Instruments have been quick off the mark regarding continuous measurement, and have already received orders from several customers for this application. Where continuous measurement of dewpoint is required Michell Instruments have the ideal instrument, Easidew On-Line.

The Easidew On-Line utilises the Michell Instruments ceramic sensor to provide stable and accurate measurement of dewpoint in the range of -100 to + 20 °C. The Easidew On-Line monitor provides a large red LED display of the dewpoint. A 4-20mA analog output is available for interfacing to data-loggers or distributed control system, and two alarms relays can be set by the user to provide indication that the gas is approaching, or is outside, the required specification.

To provide a "one-stop" service to the customer Michell Instruments can, if required, provide the Easidew On-Line already mounted within wall-mounted enclosure, and with a sampling system. This sampling system includes a filter, to protect the sensor, and a valve and flowmeter so that the appropriate sample flowrate can be set. This all in one approach requires only that the customer provide a flow of gas and the necessary pipework. This solution is particularly useful for fitting to existing medical gas dryers.

Easidew On-Line is the perfect solution for new medical gas systems or for those users with older systems wishing to ensure that they meet the new HTM 02 standards.___________________________________________________

For more information, please contact :-

Tim Landucci
Michell Instruments Limited
48 Lancaster Way Business Park,
Ely, Cambridgeshire CB6 3NW. UK
Tel: +44(0) 1353 658031 Fax: +44(0) 1353 658199
website: www.michell-instruments.co.uk

November 2006

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